This invention relates to an image search method for searching and retrieving a desired image from a memory device which stores a number of images and displaying the retrieved image on a display device.
It has become very popular in recent years to have computers execute image management of such images as photographs and drawings. In an image management system of this kind, still images such as photographs and drawings are stored in large quantity on a magnetic disk, optical disk or photomagnetic disk, a desired image is retrieved as needed and the retrieved image is displayed on a display device.
Methods available for the search and retrieval of a desired image include a method through which still images are searched one at a time and a method through which the search is performed by displaying a list of titles assigned to respective ones of the still images. With the method of searching for frames one by one, however, problems are encountered in that this method leads to operator eye fatigue and has a low search speed. With the method of search and retrieval from a title list, the images cannot be searched while being observed. Consequently, the accuracy of search is poor and the search is difficult to perform. These shortcomings shall be referred to as a first problem hereinbelow.
Magnetic disks, optical disks, photomagnetic disks and the like are large-capacity storage devices. However, since approximately 130 kilobytes are required in order to store a single image, these disks are incapable of storing a large quantity of images. This shall be referred to as a second problem.
In order to solve the first problem, an image search method has been proposed in which images 3.sub.1, 3.sub.2, . . . reduced in size and then combined are stored on a video disk 1 in advance, as shown in FIG. 1. Each of the images 3.sub.1, 3.sub.2, . . . is obtained by combining m--number (16, for example) of original images 2.sub.1, 2.sub.2, 2.sub.3, . . . 2.sub.s in horizontal and vertical directions upon reducing them in size to 1/4 in each of these directions. At the time of search, the reduced and combined images 3.sub.1, 3.sub.2, are displayed successively on the display device, a desired image is found and designated among the reduced and combined images, and the designated original image is displayed on the display device. In accordance with this method of search, an advantage over the conventional methods is that a high-speed search can be performed while the images are being displayed.
However, searching speed is only about 16 times as fast as a single-frame search. This means that in a case where a large number of images, e.g., 1600, have been stored, the reduced and combined images must be displayed 100 times in a worst-case situation. The images reduced to 1/16 must be viewed one at a time, and if the desired image is not found, then the image search must be performed in a similar manner upon displaying the next group of reduced combined images. As a result, the problem of operator eye fatigue is still encountered. Thus, there are limitations upon the method of FIG. 1 in a case where a large number of images are stored on a disk.
In order to solve the second problem, an image filing apparatus has been proposed in which the original images and the images that have been reduced and combined are both stored on a disk upon being subjected to compression coding, after which images are restored at the time of display. However, the same compression coding method is used for the original images and for the reduced and combined images. Consequently, when image compression is performed by high-compression coding, the memory capacity required in order to store the images can be decreased but the reduced and combined images cannot be restored and displayed at high speed at the time of image retrieval. As a result, search time is prolonged.